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Coefficient of Friction

by shinnsohai
Tags: dynamic friction, force, static friction
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shinnsohai
#1
Dec28-11, 12:15 PM
shinnsohai's Avatar
P: 33
1. The problem statement, all variables and given/known data
1.a block of mass 5kg moves on a rough horizontal plane with coefficient of friction (Dynamic) 0.2 under the action of a horizontal force of 30N. If the block starts from rest , find the distance it travels in the first 3 second.

2.a particle of mass 6kg,moving at 8m/s on a smooth horizontal surface, goes onto a rough horizontal surface with a coefficient of friction 0.25> Find the distance it moves across the rough surface before coming to rest.

3.This is my own question.Because I might get the concept of friction force wrongly
It's been in my mind for about 3 days thinking of it

A particle moving up a slope with a maintained speed of 1m/s
In another situation a same particle moving up the same slope with a maintained speed of 5m/s

Do the two particle use the same force?

As the Coefficient,mass,gravity,angle of slope are the same


2. Relevant equations
F/N =u(Mew)
F=ma
s=ut+1/2 at^2

Anyhow Regarding the equation,
Relating The Momentum and Force
F=ma
F=m x v/t
Ft=mv

So If The Force is 15N and the object moving at a constant velocity last for 3 seconds
Ft=mv
15(3) = MV
It will be 45 kg m/s ??




3. The attempt at a solution
1.
M=5kg
Force=30N
μDynamic = 0.2
μStatic = F/N (Force Used To Overcome the Static Friction)/(Normal Force)
= 30/(30x9.8)
= 0.1020
Initial Velocity=0
Final Velocity = 0
Time=3 seconds
Distance = Unknown

Untill This Step
What Should I Do With the two different coefficient of friction??

2.
Upon This Stage I Do Realize that I'm Getting Stupiddd
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LawrenceC
#2
Dec28-11, 12:38 PM
P: 1,195
Static friction is not an issue in this problem. Sum the forces and proceed either by impulse momentum or by Newton's Second Law and velocity-acceleration equation.
LawrenceC
#3
Dec28-11, 12:41 PM
P: 1,195
"A particle moving up a slope with a maintained speed of 1m/s
In another situation a same particle moving up the same slope with a maintained speed of 5m/s

Do the two particle use the same force?"

Yes.


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